2,2,6-Trimethyl-cyclohexanecarboxaldehyde, also known as dihydrocyclocitral, is a cycloaliphatic aldehyde of formula ##STR5##
Not only does it represent a useful intermediate in a variety of organic syntheses but it constitutes a raw material for the preparation of useful end-products for the flavor and perfume industry as well as for the preparation of pharmaceuticals, namely for carotenoids and steroids type compounds (see in this respect European Patent Application No. 118,809 published on Sept. 19, 1984).
Numerous methods for its preparation have been described in the prior art.
M. de Bottom [Bull. Soc. Chim. de France, 33, 2466-73 (1966)] has described the preparation of dihydrocyclocitral starting from 2,2,6-trimethyl-cyclohexanone according to the following reaction scheme: ##STR6##
Earlier described methods are based on the hydrogenation of cyclocitral [Helv. Chim. Acta, 31, 417 (1948) and Helv. Chim. Acta, 34, 1160 (1951)] or on the oxidation of dihydrocyclogeraniol [Helv. Chim. Acta, 23, 529 (1940) and Helv. Chim. Acta, 23, 1265 (1940)]. The substitution of a ketonic oxygen atom by an hydrogen and a formyl group, a reaction of the type EQU R.sub.2 CO.fwdarw.R.sub.2 CHCHO
represents a useful approach in organic syntheses for which several specific reactants have been developed. However none of them gives satisfactory results in the case of the transformation of sterically hindered ketones having a hydrogen atom in the alpha position to the ketonic group. E. J. Corey and M. A. Tius [Tetrahedron Letters, 21, 3535-8 (1980)] have described a method for the preparation of dihydrocyclocitral starting from cyclohexanone, precisely by means of one of these specific reagents, diphenyl-methoxy-methyl phosphine. The nature of the reactant, however, renders the industrial scale-up application of this method rather problematic.
I have now discovered that dihydrocyclocitral could be obtained according to a simple and economical process, which process has the advantage of utilizing traditional reactants.